Noise on BART: How bad is it and is it harmful?

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Published 4:00 am, Tuesday, September 7, 2010

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Noise on BART: How bad is it and is it harmful?

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On stretches of the BART system, which once boasted that its trains were "smooth, virtually noiseless and vibration-free," riders cover their ears and have to shout to be heard over the screeching, roaring and banging din.

"What?!" shouted Crystal Glantz, 44, of Alameda, smiling, as a reporter tried to interview her aboard a train hurtling through the Transbay Tube. "It's very noisy. It would be nice to be able to listen to music or have conversations."

The Chronicle surveyed the BART system, sending a reporter on all 208 miles of rails - 104 in each direction - accompanied by a handheld sound-level meter. The survey found that noise levels can reach 100 decibels - the equivalent of a jackhammer - at points in the Transbay Tube. But the tube is not the only noisy part of the system, as many riders can attest. Trains produced noise levels of 90 decibels - as loud as a diesel truck - or higher at 23 locations.

BART spokesman Linton Johnson acknowledged that the system's trains can be noisy in spots, but said a recent study gave the agency a top rating among comparable rail systems nationwide.

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"Customers riding at times may not believe it," he said, "but we're the quietest in the country."

Much of the noise on BART is caused by steel-wheeled trains repeatedly rolling over steel rails, creating microscopic ripples that produce shrill noises. BART uses two rail-grinding machines to smooth the rails and reduce noise.

What's too loud?

Noises as low as 85 decibels can cause hearing damage, according to the National Institute for Occupational Safety and Health, but that's with prolonged exposure. People can be exposed to 91 decibels for two hours before hearing damage may occur, according to the institute's recommendations. At 100 decibels, the recommended exposure limit is 15 minutes. BART riders are exposed to those noise levels only intermittently, and usually for brief periods.

"We talk about your sound exposure over a whole 24 hours," said Linda Howarth, program coordinator for Dangerous Decibels, which aims to reduce noise-caused hearing loss. "If you have a fairly quiet day and get on the subway and have a few minutes of 90 decibels or even 100 decibels, you'll be fine." But even if BART's noise isn't a hearing hazard, it can be annoying.

"People can be irritated by 70 decibels or 80 decibels," Howarth said. BART monitors decibel levels inside trains to protect train operators, who are exposed to high noise levels four to five hours a day, Johnson said. Operators are encouraged to wear hearing protection, he said.

The worst spots

So, where is BART the most irritating? Not surprisingly, the Transbay Tube, heading westbound, had the highest reading of 100 decibels several times, causing some riders to cover their ears, and drowning out conversation.

"It's way too loud," said Bob Haeger, 54, a Berkeley attorney familiar with the cacophony of the tube. "The stress of listening to the noise is tiring."

Haeger said he wishes BART would slow trains in the Tube to diminish the din - a move that would probably annoy most riders more than the noise.

While the Transbay Tube - where trains travel up to 80 mph in concrete enclosures - is understandably noisy, the ride was nearly as loud eastbound between the Glen Park and 24th Street Mission stations, where the sound hit 99 decibels. Seven other stretches - Balboa Park to Glen Park, 24th Street Mission to 16th Street Mission, 16th Street Mission to Civic Center, the Transbay Tube westbound, Embarcadero to Montgomery Street, Rockridge to Orinda and North Concord/Martinez to Pittsburg/Bay Point - exceeded 95 decibels.

Noise levels, of course, vary widely depending on the train's speed, the rider's location, whether the train is accelerating or braking, whether another train is passing, and the number of passengers aboard.

Johnson said trains are the noisiest when they're heading up or down inclines or traveling around curves and produce ear-piercing screeching sounds. Many riders, he said, are bothered more by the high pitch of the noise than the loudness. Many riders don't realize it, Johnson said, but the Transbay Tube curves as it passes beneath the Bay Bridge. The stretch between Civic Center and Balboa Park also contains curves.

Another big factor, predictably, is whether the tracks are underground. Nearly all of the 20 noisiest stretches were in tubes, tunnels or subways, where the surrounding concrete walls trap the sound. Above-ground tracks were much quieter.

A little peace

The quietest ride on the BART system was between the Hayward and South Hayward stations, where the southbound train zipped along smoothly - on flat ground and a berm - recording a maximum sound level of just 73 decibels, about as loud as a hair dryer.

The northbound train on that same stretch was the next quietest at 77 decibels. Noise levels stayed below 80 decibels over five other stretches of track - Union City to Fremont, Colma to South San Francisco, Castro Valley to Dublin/Pleasanton, Hayward to Bay Fair and Pleasant Hill to Walnut Creek.

While it's impossible not to notice the noise, many BART riders said they take it in stride.

"It's really just a short period of time," said Rafael Torres, 50, of Antioch, a restaurant manager. "You just have to put up with it, I guess."

Hearing expert Howarth advises riders disturbed by the noise to listen to their instincts, and take action.

"If it sounds too loud for you, it probably is," she said. "So do something about it: Wear earplugs, or put your fingers in your ears if that's all you have."